Scattering of ultrasound by biological tissues is not yet fully understood. Our long term objective is to gain such an understanding with the aim of increasing the utility of ultrasonic diagnostic procedures. In order to achieve this objective we will work on the following problem areas: We will first work on determining by analysis and computer simulations the extent of phase-cancellation artifacts in the measurement of scattered ultrasonic fields from different tissues. It is now well known that when scattered fields are measured with transducers that are many wavelengths in diameter, serious errors may arise due to phase cancellation. Our analysis and computer simulations should help us determine the optimum equipment parameters for experimental studies on scattered ultrasound. In our analytical and computer simulation work we will perform statistical analyses on scattered fields and calculate some measure of the variation in the magnitude of the field and the mean distance between adjacent maximas and minimas. By using Monte Carlo techniques we will also perform computer simulations to determine the extent of multiple scattering in different tissues. Such techniques have already proved successful in handling the multiple scattering problems in atmosphere. We will also be interested in studying the effect of amplitude shading of the receiving transducers on the degree of phase cancellations. In particular, we will be interested in Gaussian transducers. And, finally, we will be interested in studying the feasibility of using fourier imaging for directly obtaining the images of the scattering centers.